Friday 11 January 2013 12.49 EST
First published on Friday 11 January 2013 12.49 EST

The Bumi saga deepened on Friday with allegations that hackers broke into the chairman's computer to steal documents used to spark a crisis at the mining group.

An investigation by a private security company suggests hackers retrieved information from Samin Tan's laptop, which was then sent to a Bumi director by an unnamed "whistleblower", plunging the company into chaos.

Last October, Bumi launched an investigation into the origin of the whistleblower's report, which alleged financial dishonesty at Bumi's main affiliate, one of Indonesia's largest coal producers. Tan accused Bumi founder Nat Rothschild of reading his emails, while the company's Indonesian backers – the Bakrie family – alleged "phones and emails had been hacked". Rothschild has denied having access to Tan's emails and says he brought the whistleblower's report, that had been provided to him on an unsolicited basis, to the attention of Bumi's independent non-executives. Rothschild said on Friday he knew nothing of the events described in the report into hacking.

The investigation – first published by the Times on Friday – says hackers emailed Tan posing as "Steve", a researcher associated with Wikipedia. "Steve" said Wikipedia wanted to publish an article on the chairman and asked for him to comment. The report states: "It should be noted this is fundamentally suspicious; it is not standard Wikipedia policy to contact individuals with regards to articles."

The emails contained links to articles about Tan, which, when followed, are thought to have infected his computer with malicious software. The whistleblower report emerged afterwards, containing information thought only to be held on Tan's computer.

That report kicked off the crisis at Bumi, which was forced to hire lawyers to investigate the allegations. Bumi shares crashed and the Bakrie family offered to sever their ties with the London-listed group, by paying $1.29bn (£800m) in cash to buy Bumi's mines and cancel their shares in the investment vehicle. The Indonesians spiced up their proposal with a separate suggestion that Rothschild should give up a stake in Bumi worth upwards of £40m.

Rothschild opposed all aspects of the offer and announced his resignation from the Bumi board – although it later emerged that both Tan and the company's non-executive, the former British diplomat Lord Renwick, had threatened to quit if Rothschild chose to stay.

Now Rothschild is trying to wrest control of the group and has called for a shareholder meeting to remove 12 of the current 14 directors on the Bumi board. The company has agreed to hold the meeting, which is thought to be scheduled for February. Among the shareholders, Schroders, which owns more than 4% of the company, is said to be backing Rothschild.

Rothschild led the London flotation of Bumi two years ago, when it was known as Vallar and the shares began trading at £10 each. The shares inched lower on Friday to 304p. The company started life as a £700m cash shell intended to make acquisitions in the mining industry and was renamed Bumi after taking a 29% stake in the mining business controlled by the Bakrie family.

The saga has fascinated the City, particularly as Rothschild had worked furiously to become known as a serious financier and shed the playboy image of his university days, when he was famously a member of Oxford University's Bullingdon Club at the same time as the chancellor, George Osborne.